Lecture Link: MRSA, MRSP, and MRSS in dogs—What can we do?

By now most of us have heard of the increasing incidence of methicillin-resistant staphylococci infections in dogs. It is most commonly associated with methicillin-resistant Staphylococcus pseudintermedius (MRSP), but other staphylococci may be involved, including methicillin-resistant Staphylococcus aureus (MRSA) and Staphylococcus schleiferi (MRSS). Andrew Hillier, BVSc, MACVSc, DACVD, a professor at The Ohio State University College of Veterinary Medicine, discussed this problem in a presentation at the 7th World Congress of Veterinary Dermatology held this summer in Vancouver.

Dr. Hillier explained the steps involved in the proper selection of antibiotics for superficial bacterial pyoderma in dogs. These guidelines, like the previous guidelines published concerning antibiotic use for treating urinary tract infections (which can be found at hindawi.com/journals/vmi/2011/263768), are the result of the International Society for Companion Animal Infectious Disease (ISCAID) Antimicrobial Guidelines Working Group, consisting of veterinary internists, pharmacologists, microbiologists, and dermatologists (iscaid.org).

Dr. Hillier suggested the following when managing a case of superficial bacterial folliculitis in dogs:

1. Identify and treat the underlying cause.

2. Perform skin scrapings to identify Demodex species mites.

3. Perform cytology to confirm a bacterial component.

4. If possible, use disinfectants and topical antimicrobials as the sole treatment. If this is not possible, at least use topical therapy to shorten the length of time systemic antibiotics need to be used.

5. Use empirical therapy in nonrecurrent cases or recurrent cases that have successfully responded to previous treatment. Select a drug from the list of first-tier medications. This list includes clindamycin, first-generation cephalosporins, potentiated sulfonamides, erythromycin, lincomycin, and doxycycline.

In cases that fail to respond to appropriate treatment with a first-tier antibiotic, perform a bacterial culture. When selecting an antibiotic based on a culture result, a sensitive second-tier antibiotic should only be used if the organism is resistant to all first-tier antibiotics or the animal cannot tolerate any of the first-tier drugs (or the owner is unable to administer them). The second-tier antibiotics include third-generation cephalosporins (cefovecin and cefpodoxime), any fluoroquinolone,* chloramphenicol, and rifampin.

6. Never use third-tier antibiotics (vancomycin, linezolid) without consultation with a specialist.

7. Continue treatment for a minimum of 21 days. The end point is seven days beyond clinical resolution based on the practitioner's examination, not the owner's observation.

*Note: In a presentation at the same meeting titled "Antimicrobial therapy considerations for successful treatment of dermal infections," Mark Papich, DVM, MS, DACVCP, explained that ciprofloxacin should not be used in dogs because of the wide variation in absorption (Papich MG. Ciprofloxacin pharmacokinetics and oral absorption of generic ciprofloxacin tablets in dogs. Am J Vet Res 2012;73[7]:1085-1091). To get appropriate blood concentrations you would need to dose ciprofloxacin at 12 to 52 mg/kg. This dosage is for highly susceptible (low minimum inhibitory concentration [MIC]) organisms, not the ones with higher MICs.